1. Field of the Invention
This invention relates to a device for detecting the light transmissivity of an object to be detected and a recording and/or reproducing apparatus using the same.
2. Description of the Related Art
The detecting devices of the above stated kind have been known including the tape-end detecting device which is used for a recording and/or reproducing apparatus such as a video tape recorder (hereinafter referred to as VTR). In the case of the VTR using such a device, an opaque magnetic tape which is placed within a cassette is provided with transparent leader tape parts at both ends thereof. Either a light emitting element or a light receiving element is inserted into the cassette. Meanwhile a light receiving element or a light emitting element is opposed to the inserted element across the magnetic tape. The end of the tape is thus arranged to be detected by detecting the emitted light of the light emitting element passing through the leader tape part by means of the light receiving element.
However, the photo-sensitive element which is employed as the light receiving element is responsive to light of any kind. If the light receiving element happens to be irradiated over a certain length of time by a leak of an external light inside the VTR, therefore, the tape would be erroneously determined to have come to its end. In the event of a VTR arranged to stop the tape from travelling upon detection of the end thereof, the tape travel would untimely be brought to a stop during the process of recording or reproduction by such erroneous detection due to an external light. To avoid this, the VTR must be designed to shut out any external light or to have the light receiving element in a position to be free from any external light. However, this requirement has narrowed allowable latitude in designing the VTR.